1. Technical Field
Embodiments relate to a nonvolatile memory device, and more particularly, to a nonvolatile memory device which has a single-layered gate.
2. Related Art
Various structures have been suggested for the memory cell of a nonvolatile memory device capable of electrically programming and erasing data, for example, an EEPROM. In nonvolatile memory devices, the data stored in a memory cell is not erased and is retained even when power is interrupted. In the conventional art, a stacked gate structure has been generally adopted as the EEPROM memory cell structure. The stacked gate structure includes a floating gate for storing data and a control gate formed over the floating gate. A dielectric layer is interposed between the floating gate and the control gate. Recently, as the size of electronic devices has decreased and fabrication technologies for semiconductor devices are developed, a system-on-chip (SOC) has been highlighted as a key part of an up-to-date digital product. In a SOC, various types of semiconductor devices are installed in a single semiconductor chip so that the chip can perform various functions. For example, logic devices and memory devices may be formed together in a single semiconductor chip. Accordingly, fabrication technologies for an embedded type EEPROM, which is embedded in a system-on-chip (SOC), is in demand.
In order to fabricate an embedded type EEPROM, logic devices and an EEPROM are fabricated through the same processing steps. Logic devices generally adopt transistors with a single gate structure. In contrast, an EEPROM generally employs a stacked gate structure. Therefore, fabrication procedures for integrating an EEPROM along with logic devices in the same substrate are complicated. In order to address this issue, a single-layered-gate EEPROM has been increasingly adopted as for embedded type EEPROM. In the case where the single-layered-gate EEPROM is formed by using a general CMOS (complementary metal oxide semiconductor) process, which is employed to fabricate logic devices, a system-on-chip (SOC) may be easily realized.